Nanoribbons Research Articles

Ultra-thin metal-organic framework nanoribbons.

Structure engineering of metal-organic frameworks (MOFs) at the nanometer scale is attracting increasing interest due to their unique properties and new functions that normally cannot be achieved in bulk MOF crystals. Here, we report the preparation of ultra-thin MOF nanoribbons (NRBs) by using metal-hydroxide nanostructures as the precursors. Importantly, this general method can be used to synthesize various kinds of ultra-thin MOF NRBs, such as MBDC (M = Co, Ni; BDC = 1,4-benzenedicarboxylate), NiCoBDC, CoTCPP (TCPP = tetrakis(4-carboxyphenyl)porphyrin) and MIL-53(Al) NRBs. As a proof-of-concept application, the as-prepared ultra-thin CoBDC NRBs have been successfully used as a fluorescent sensing platform for DNA detection, which exhibited excellent sensitivity and selectivity. The present strategy might open an avenue to prepare MOF nanomaterials with new structures and unique properties for various promising applications.

Shape and fluctuations of frustrated self-assembled nano ribbons

Self-assembly is an important process by which nontrivial structures are formed on the sub-micron scales. Such processes are governed by chemical and physical principles that dictate how the molecular interactions affect the supramolecular geometry. Currently there is no general framework that links between molecular properties and the supramolecular morphology with its size parameters. Here we introduce a new paradigm for the description and analysis of supramolecular structures that self-assemble via short-range interactions. Analysis of molecular interactions determines inputs to the theory of incompatible elasticity, which provides analytic expressions for supramolecular shape and fluctuations. We derive quantitative predictions for specific amphiphiles that self-assembled into chiral nanoribbons. These are quantitatively confirmed experimentally, revealing unique shape evolution, unusual mechanics and statistics, proving that the assemblies are geometrically incompatible. The success in predicting equilibrium and statistics suggests the approach as a new framework for quantitative study of a large variety of self-assembled nanostructures.

Electron enrichment of zigzag edges in armchair–oriented graphene nano–ribbons increases their stability and induces pinning of the Fermi level

Zigzag edges of neutral armchair–oriented Graphene Nano–Ribbons show states strongly localized at those edges. They behave as free radicals that can capture electrons during processing, increasing ribbon's stability. Thus, charging and its consequences should be investigated. Total energy calculations of finite ribbons using spin–polarized Density Functional Theory (DFT) show that ribbon's charging is feasible. Energies for Pariser-Parr-Pople (PPP) model Hamiltonian are compatible with DFT allowing the study of larger systems. Results for neutral ribbons indicate: i) the fundamental gap of spin–polarized (non–polarized) solutions is larger (smaller) than experimental data, ii) the ground state is spin–polarized, a characteristic still not observed experimentally. Total energy of GNRs decreases with the number of captured electrons reaching a minimum for a number that mainly depends on zigzag–edges size. The following changes with respect to neutral GNRs are noted: i) the ground state is not spin–polarized, ii) fundamental gap is in-between that of spin–polarized and non–polarized solutions of neutral ribbons, iii) while in neutral ribbons valence and conduction band onsets vs. the fundamental gap, linearly and symmetrically approach mid–gap with slope 0.5, charging induces Fermi level pinning, i.e., the slopes of the valence and conduction bands being about 0.1 and 0.9, in agreement with experiment.

Study on the element segregation and Laves phase formation in the carbon nanotubes reinforced IN718 superalloy by laser cladding

Electroless plating of Ni on the surfaces of multi-walled carbon nanotubes (MWCNTs) with two types of thicknesses were achieved. The structural evolution of MWCNTs in the laser cladding processing was investigated. It is observed that the MWCNTs can partially survive in the laser additive layers, but most of the tubes are unzipped, forming the graphene nano sheets (GNSs) and fragments. It is also found that the graphene fragments are inter-bonded with the neighboring ones, resulting in the formation of large porous carbon nano ribbons (CNRs). Due to the high surface area of the GNSs and CNRs, the element segregation and Laves phase formation in the laser cladded IN718 superalloy are suppressed significantly. With the thickness-increase of the Ni layer, the perfection of the graphene structure in the GNSs and CNRs is enhanced, and correspondingly, the depression effect on the element segregation and Laves phase formation of IN718 superalloy is improved.

Theoretical study on boron-nitrogen containing analogues of 6,6,18-graphdiyne

The structures and electronic properties are explored for the several boron-nitrogen (BN) containing analogues of 6,6,18-graphdiyne including two-dimensional (2D) sheets and one-dimensional (1D) nanoribbons (NRs) using the self-consistent-field crystal orbital method. The frequency analyses reveal the BN-containing materials are stable structures due to no existence of imaginary frequency. The calculations show that BN doped 6,6,18-graphdiyne sheets are semiconductors with wide band gaps. The semiconducting property is kept for the corresponding 1D NRs except for the NRs constructed only by BN units with zigzag edges. The calculated carrier mobilities of the 2D sheets can reach the order of 105 cm2 V−1 s−1 and are anisotropic. As for the 1D NRs, the carrier mobilities increase monotonously with increasing of the NR widths and are 1–2 orders of magnitude lower than those of the corresponding 2D sheets for the armchair NRs, but the situation is different for the zigzag NRs.

Growth of Molybdenum Trioxide Nanoribbons on Oriented Ag and Au Nanostructures: A Scanning Electron Microscopy (SEM) Study.

We report the growth of molybdenum trioxide (MoO3) nanoribbons (NRs) on epitaxial Ag and oriented Au nanostructures (NSs) using an ultra-high vacuum (UHV)-molecular beam epitaxy (MBE) technique at different substrate temperatures. An approximately 2 nm silver (Ag) film has been deposited at different growth temperatures (using UHV-MBE) on cleaned Si(100), Si(110), and Si(111) substrates. For faceted Au NSs, an approximately 50 nm Au film has been deposited (using high-vacuum thermal evaporation) on a Si(100) substrate with a native oxide layer at the interface and the sample was annealed in low vacuum (≈10-2) and at high temperature (≈975°C). Scanning electron microscopy measurements were performed to determine the morphology of MoO3/Ag and MoO3/Au composite films. From energy dispersive X-ray spectroscopy elemental mapping and line scans it is found that faceted Au NSs are more favorable for the growth of MoO3 NRs than epitaxial Ag microstructures.

High-Performance Nanofloating Gate Memory Based on Lead Halide Perovskite Nanocrystals.

Lead halide perovskites have been extensively investigated in a host of optoelectronic devices, such as solar cells, light-emitting diodes, and photodetectors. The halogen vacancy defects arising from the halogen-poor growth environment are normally regarded as an unfavorable factor to restrict the device performance. Here, for the first time, we demonstrate the utilization of the vacancy defects in lead halide perovskite nanostructures for achieving high-performance nanofloating gate memories (NFGMs). CH3NH3PbBr3 nanocrystals (NCs) were uniformly decorated on the CdS nanoribbon (NR) surface via a facile dip-coating process, forming a CdS NR/CH3NH3PbBr3 NC core-shell structure. Significantly, owing to the existence of sufficient carrier trapping states in CH3NH3PbBr3 NCs, the hybrid device possessed an ultralarge memory window up to 77.4 V, a long retention time of 12 000 s, a high current ON/OFF ratio of 7 × 107, and a long-term air stability for 50 days. The memory window of the device is among the highest for the low-dimensional nanostructure-based NFGMs. Also, this strategy shows good universality and can be extended to other perovskite nanostructures for the construction of high-performance NFGMs. This work paves the way toward the fabrication of new-generation, high-capacity nonvolatile memories using lead halide perovskite nanostructures.

Tuning Electrical and Raman Scattering Properties of Cadmium Sulfide Nanoribbons via Surface Charge Transfer Doping

Surface charge transfer doping (SCTD) has emerged as an efficient approach to tune the electrical and optical properties of semiconductor nanostructures. As an important II–VI semiconductor, cadmium sulfide (CdS) nanostructures possess superior optoelectronic properties. However, the SCTD on the CdS nanostructures remains a challenge, and the underlying mechanism for optical property modulation is unclear. Herein, we demonstrate that both the electrical and Raman scattering properties of CdS nanoribbons (NRs) can be tuned by using MoO3 and benzyl viologen (BV) as surface dopants. The MoO3 (or BV) molecules, which have a high work function (or strong reducing capability), can extract (or inject) electrons from (or into) the CdS NRs because of the large difference in energy levels, leading to electron depletion (or accumulation) within the CdS NRs. By controlling the amount of surface dopants, the electron concentration as well as resistivity of the CdS NRs can be readily modulated. Significantly, Raman sca...

Electronic and magnetic properties of CrI3 nanoribbons and nanotubes**Project supported by the National Key R&D Program of China (Grant No. 2017YFA0206301) and the Major Program of Aerospace Advanced Manufacturing Technology Research Foundation NSFC and CASC, China (Grant No. U1537204).

CrI3 in two-dimensional (2D) forms has been attracting much attention lately due to its novel magnetic properties at atomic large scale. The size and edge tuning of electronic and magnetic properties for 2D materials has been a promising way to broaden or even enhance their utility, as the case with nanoribbons/nanotubes in graphene, black phosphorus, and transition metal dichalcogenides. Here we studied the CrI3 nanoribbon (NR) and nanotube (NT) systematically to seek the possible size and edge control of the electronic and magnetic properties. We find that ferromagnetic ordering is stable in all the NR and NT structures of interest. An enhancement of the Curie temperature TC can be expected when the structure goes to NR or NT from its 2D counterpart. The energy difference between the FM and AFM states can be even improved by up to 3–4 times in a zigzag nanoribbon (ZZNR), largely because of the electronic instability arising from a large density of states of iodine-5p orbitals at EF. In NT structures, shrinking the tube size harvests an enhancement of spin moment by up to 4%, due to the reduced crystal-field gap and the re-balance between the spin majority and minority populations.

O2 atmospheric annealing-tunable defects in ionic oxide MgO nanoribbons

An isotropic lattice shrinkage (lattice volume ratio ∼−0.462%) structure was reported in cubic magnesium oxide (MgO) nanocrystals, favoring the enhanced electron correlation. Upon postannealing in an O2 atmosphere, significant changes in photoluminescence spectra were detected in pristine MgO nanoribbons (NRs): a substantial reduction in F+-type centers (Fc) and an increase in a previously unknown peak at 358 nm (3.46 eV) which we attribute to a small polaron (SP) complex as a deep acceptor. A reduced diluted magnetism was found in the O2-annealed MgO NRs. A room temperature electron paramagnetic resonance signal at g ∼ 2.0959 revealed the presence of an unpaired electron trapped in the MgO NRs and a weak broad signal shift at g ∼ 2.0888, suggesting a reduced anisotropic spin–orbit coupling in the O2-annealed MgO NRs. Finally, a view on competition between Fc and SP was proposed: the Fc defect favors FM, and the SP complex leads to reduced FM in MgO NRs. The findings provide new insight into the origin and defect engineering of d0 diluted magnetism in MgO (spin from MgO), and this physical mechanism would be generally applied to other ionic oxide family materials in the field.

Polar-Induced Selective Epitaxial Growth of Multijunction Nanoribbons for High-Performance Optoelectronics.

Semiconductor heterostructures are basic building blocks for modern electronics and optoelectronics. However, it still remains a great challenge to combine different semiconductor materials in single nanostructures with tailored geometry and chemical composition. Here, a polar-induced selective epitaxial growth method is reported to alternately grow CdS and CdS xSe1- x heterostructure nanoribbons (NRs) side by side in the lateral direction, with the heterointerface (junction) number to be well controlled. Transmission electron microscopy (TEM) and spatial-resolved μ-PL spectra are employed to characterize the heterostructure NRs, which indicate that the achieved NRs are high-quality heterostructures with sharp interfaces. Kelvin probe force microscopy (KPFM) and femtosecond pump-probe characterizations further confirm the efficient charge-transfer process across the interfaces in the multijunction NRs. Photodetectors based on the achieved NRs are realized and systematically investigated, demonstrating junction number-dependent optoelectronic response behaviors. NRs with more junctions exhibit more superior device performances, reflecting the important roles of the high-quality interface regions. Based on this multijunction NRs device, high on-off ratio (107) and remarkable responsivity (1.5 × 105 A/W) are demonstrated, both of which represent the best results compared to the reported CdS, CdSe, and their heterostructures. These novel multijunction NRs may find broad applications in future integrated photonics and optoelectronics devices and systems.

Microscopy and spectroscopy study of nanostructural phase transformation from β-MoO3 to Mo under UHV – MBE conditions

We report a simple reduction of molybdenum oxide (β-MoO3) grown on reconstructed Si(100) by thermal annealing in ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). By increasing the substrate temperature during deposition or the annealing temperature after growth, the morphologies of as-deposited structures were found to vary from nanoribbons (NRs) of β-MoO3 to nanoparticles (NPs) of Mo. The change in morphologies have been associated with a structural transition from β-MoO3 to MoO2 at 400 °C and MoO2 to Mo at 750 °C. The in-situ X-ray photoelectron spectroscopy (XPS) measurements revealed a shift of the Mo 3d peaks towards lower binding energies, representing the reduction in Mo oxidation states until a pure Mo 3d peak at 750 °C was observed. The ex-situ KPFM measurements showed a decrease in the local work function (Φ) (from ≈ 5.27 ± 0.05 eV to ≈ 4.83 ± 0.05 eV) with increasing substrate temperature. A gradual reduction of the band gap from ≈ 3.32 eV for β-MoO3 NRs to zero band gap for Mo NPs is also observed during the annealing up to 750 °C.

Influence of growth temperature on titanium sulphide nanostructures: from trisulphide nanosheets and nanoribbons to disulphide nanodiscs.

We report the fabrication and characterization of titanium sulphide nanostructures using a chemical vapour transport (CVT) method. In CVT, reactions occur between titanium and sulphur powder in the vapor phase for TiSx nanostructure growth. Systematic studies on the effect of temperature, consequent structural evolution and optical properties were investigated by various characterization techniques. A series of experiments were performed by maintaining a fixed compositional ratio (1 : 3) of Ti and S within a temperature range from 400 °C to 650 °C. On increasing the temperature from 400 °C to 650 °C; a gradual change in morphology was obtained from nanosheets (NS) to mixed phase nanoribbons and nanosheets (NS: NR), nanoribbons (NR), and nanodiscs (ND) of titanium sulphide, which was confirmed using SEM/TEM analysis. Then, the composition of titanium sulphides was studied using XRD, EDX and Raman spectroscopic techniques and it is observed that NS, NR and NS: NR have the composition ratio of TiS3 whereas ND has a ratio of TiS2. The phenomenon of decomposition of TiS3 into TiS2 at elevated temperatures was explained using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) along with pictorial representations. The optical properties of the prepared TiS3/TiS2 nanostructures were studied using UV-vis and photoluminescence spectroscopy. It is concluded that composition ratio of Ti and S as well as the temperature variation plays a crucial role in the formation of different Ti–S nanostructures with unique optical, electronic and thermal properties.

Hafnium oxide nanoparticles fabricated by femtosecond laser ablation in water

We report the fabrication of colloidal hafnia nanoparticles (NPs) and nanoribbons (NRs) in deionized water achieved by femtosecond laser ablation. The average size of NPs and NRs varied in the range 13.5–18.0 nm and 10–20 nm, respectively, with varying input laser energy. At lower energies, the NPs were observed to be in pure monoclinic phase of HfO2. However, at higher input energies, interestingly, both monoclinic and hexagonal phases corresponding to HfO2 and Hf6O were observed. Hf6O is otherwise expected only at high pressures.

Utilizing Graphene Nano-Ribbon Transistor in Data Converters: A Comparative Study

In recent years, efforts to perform more processing operation on a silicon chip have made a strong enthusiasm for making the circuit components smaller in order to reduce the power and increase the speed. Due to silicon constraints, there will be no possibility to follow Moore's law. That's why we should look for an alternative to silicon. Therefore, due to high mobility, high current density, and low noise, the study on Graphene Nano Ribbon (GNR) began. ADCs and DACs have a major share in the electronics industry. An ADC prepares signals for the digital world and microprocessor processing. There are different methods for converting analog to digital signals. Among them, due to unique features such as high speed; Flash ADC has attracted the attention of designers. In this research first, a model for simulating of the GNR field effect transistor (GNRFET), is introduced. Then, this model is used to design a flash ADC. The results of this study indicate that the designed circuit has a desirable performance as an ADC. In addition, compared to a same Si-CMOS sample, errors such as DNL, INL, Offset, and Full scale are reduced. Moreover, GNR-based ADC shows less power consumption. The maximum and minimum power consumption are equal to 27.8% and 17.6% which corresponds to 5-bit and 4-bit GNR-based flash ADCs compared with their CMOS counterpart. Moreover, this research indicates a significant improvement in the delay that is at least 86.3% and maximum 88.6% which corresponds to 5-bit and 3-bit GNR-based flash ADCs.

Strain-optoelectronic coupling properties of externally deformed nanoribbons with embedded quantum well

Strain-engineering provides a critical mechanism for tuning the band structure of quantum wells (QWs). However, due to the inherent rigidity of the semiconductor materials, the strain induced by lattice-mismatch is restricted to be invariable, uniform, thus cannot be subject to direct mechanical loading processes. Therefore, the flexible nanoribbons (NRs) in a variety of configurations offer entirely new research perspectives in modulation of the optoelectronic characteristic of QWs by curvature-induced inhomogeneous strain. In this paper, we propose a strategy to fabricate the QW layer embedded in uniaxially wavy NRs. To thoroughly figure out the internal strain-optoelectronic coupling mechanism, we establish a simple and accurate calculation model for externally deformed QW NRs using the eight-band k·p perturbation method for the first time. Luttinger-Kohn-Pikus-Bir Hamiltonian (LKPBH) for strained semiconductor is adopted and solved by finite-difference method (FDM). Theoretical calculations reveal inclined band edges, which result in the quantum-confined stark effect (QCSE) in the bended QW NRs. Continuously and periodically varied band gap of the wavy QW is revealed with a blue-shift from peak to valley of the sample NR, which agrees well with the μ-photoluminescence measurements. Further adjustments of the external configuration are explored to study the impact of the larger deformed structure on the curvature and band gap of the wavy QW within the confinement of the fracture limit.

Preparation of graphene nanoribbons (GNRs) from twisted structure carbon nanotubes using unzipping technique

This work deals with the preparation of graphene nano ribbons (GNRs), which are small bars or strips of graphene with narrow range width less than 50 nm and one atom thick sheet (approximately 140 °A). This material has many applications in electronics, polymer composite, contrast agent bio-imaging and others. This material was prepared from twisted structure of carbon nanotubes CNTs using oxidation process by acids and breaking down by high frequency ultrasonication (sonochemical unzipping). Pre-prepared twisted CNTs were characterized by scanning electron microscope (HRSEM) before treatment. The size, morphology, crystallinity of prepared graphene nanoribbons was also investigated using transmission electron microscope, high resolution transmission electron microscope, and X-ray diffraction and particle size analyzer. The results showed of formation of GNRs with narrow width as lower than 29 nm and uniform sizes. X-ray diffraction reveals Bragg reflections corresponding to the lattice planes (002), (100), (101), (004), and (110) matched with hexagonal system of graphite.

Ferromagnetism of 1T'-MoS2 Nanoribbons Stabilized by Edge Reconstruction and Its Periodic Variation on Nanoribbons Width.

Nanoribbons (NRs) of two-dimensional (2D) materials have attracted intensive research interests because of exotic physical properties at edges as well as tunable properties via width control. In this paper, using density functional theory (DFT) calculations, we discover sensitive dependence of magnetic properties of 1T'-MoS2 NRs, that is, periodic variation of magnetic moments between 0.1 and 1.2 μ B, on NR width (even or odd number of MoS2 units). Our results reveal that a special edge reconstruction, which is not recognized before, stabilizes the ferromagnetic (FM) ground state. Our results also suggest that the FM state could be stable under ambient condition. This study indicates a promising means to integrate multiple magnetic units for small-scale functional devices, such as information storage and spintronics, on a single piece of MoS2 NR by designing segments with different width.

TFET I-V characteristics made of bi layer Armchair Grafene Nano Ribbon (AGNR)

The dispersion energy of bi layer arm chair grafene nano ribbon (AGNR) have been calculated using the Tight Binding method. This is used to analyze the characteristics of the device relating the voltage-current in the Tunnel Field Effect Transistor (TFET). The current’s Landauer is used for the theoretical approach of the output properties of the generated device, and the use of the Gauss Quadrature method to calculate the current on the TFET device. The result show that the current of drain linear to the wide of ribbon.

Pressure-Induced Phase Engineering of Gold Nanostructures.

Although phase engineering of a noble metal, gold (Au), is of critical importance for both fundamental research and potential application, it still remains a big challenge in wet-chemical syntheses. In this work, we report the irreversible transformation from the hexagonal 4H to face-centered cubic ( fcc) phase in Au nanoribbons (NRBs) through high pressure treatment, which has not been discovered in metals. The relative percentage of 4H and fcc phases in the recovered Au NRBs depends directly on the peak pressure applied to the original 4H Au NRBs, enabling a phase engineering of Au nanostructures. Interestingly, compared to the pure 4H Au NRBs, the crystal-phase-heterostructured 4H/ fcc Au nanorods require less energy to complete the phase transition process with a lower transition pressure and in a narrower range. Finally, the atom-based transformation pathway during the 4H-to- fcc phase transition is revealed experimentally, which is supported by the first-principle calculations. This work not only demonstrates the stability of 4H Au nanostructure and the pressure-induced 4H-to- fcc transition mechanism but also provides a strategy for the phase engineering of noble metal nanostructures.